1. I NTERNET A PPLICATIONS Chapter 7

2. 22 L ECTURE O VERVIEW Internet Concepts Web data formats HTML, XML, DTDs Introduction to three-tier architectures The presentation layer HTML forms; HTTP Get and POST, URL encoding; Javascript; Stylesheets. XSLT The middle tier CGI, application servers, Servlets, JavaServerPages, passing arguments, maintaining state (cookies)

3. 33 U NIFORM R ESOURCE I DENTIFIERS Uniform naming schema to identify resources on the Internet A resource can be anything: Index.html mysong.mp3 picture.jpg Example URIs: http://www.cs.wisc.edu/~dbbook/index.html mailto:webmaster@bookstore.com

4. 44 S TRUCTURE OF URI S http://www.cs.wisc.edu/~dbbook/index.html URI has three parts: Naming schema (http) Name of the host computer (www.cs.wisc.edu)www.cs.wisc.edu Name of the resource (~dbbook/index.html) URLs are a subset of URIs

5. 55 H YPERTEXT T RANSFER P ROTOCOL What is a communication protocol? Set of standards that defines the structure of messages Examples: TCP, IP, HTTP What happens if you click on www.cs.wisc.edu/~dbbook/index.html? www.cs.wisc.edu/~dbbook/index.html 1. Client (web browser) sends HTTP request to server 2. Server receives request and replies 3. Client receives reply; makes new requests

6. 66 S OME R EMARKS A BOUT HTTP HTTP is stateless No “sessions” Every message is completely self-contained No previous interaction is “remembered” by the protocol Tradeoff between ease of implementation and ease of application development: Other functionality has to be built on top Implications for applications: Any state information (shopping carts, user login- information) need to be encoded in every HTTP request and response! Popular methods on how to maintain state: Cookies Dynamically generate unique URL’s at the server level

7. 77 HTTP Client to Server: GET ~/index.html HTTP/1.1 User-agent: Mozilla/4.0 Accept: text/html, image/gif, image/jpeg Server replies: HTTP/1.1 200 OK Date: Mon, 04 Mar 2002 12:00:00 GMT Server: Apache/1.3.0 (Linux) Last-Modified: Mon, 01 Mar 2002 09:23:24 GMT Content-Length: 1024 Content-Type: text/html Barns and Nobble Internet Bookstore Our inventory: Science The Character of Physical Law...

8. 88 HTML Barns and Nobble Internet Bookstore Our inventory: Science The Character of Physical Law Author: Richard Feynman Published 1980 Hardcover Fiction Waiting for the Mahatma Author: R.K. Narayan Published 1981 The English Teacher Author: R.K. Narayan Published 1980 Paperback

9. 99 L ECTURE O VERVIEW Internet Concepts Web data formats HTML, XML, DTDs Introduction to three-tier architectures The presentation layer HTML forms; HTTP Get and POST, URL encoding; Javascript; Stylesheets. XSLT The middle tier CGI, application servers, Servlets, JavaServerPages, passing arguments, maintaining state (cookies)

10. 10 XML – T HE E XTENSIBLE M ARKUP L ANGUAGE Extensible Limitless ability to define new languages or data sets Markup Notes or meta-data that describe your data or language Language A way of communicating information

11. 11 XML – S TRUCTURE XML: Confluence of SGML and HTML Xml looks like HTML Xml is a hierarchy of user-defined tags called elements with attributes and data Data is described by elements, elements are described by attributes … closing tag attribute attribute valuedata open tag element name

12. 12 XML: A N E XAMPLE Richard Feynman The Character of Physical Law 1980 R.K. Narayan Waiting for the Mahatma 1981 R.K. Narayan The English Teacher 1980

13. 13 XML – W HAT ’ S T HE P OINT ? You can include your data and a description of what the data represents This is useful for defining your own language or protocol Example: Chemical Markup Language 234.5 … XML design goals: XML should be compatible with SGML It should be easy to write XML processors The design should be formal and precise

14. 14 XML – E LEMENTS … Xml is case and space sensitive Element opening and closing tag names must be identical Opening tags: “ ” Closing tags: “ ” Empty Elements have no data and no closing tag: They begin with a “ ” closing tag attribute attribute valuedata open tag element name

15. 15 XML – A TTRIBUTES … Attributes provide additional information for element tags. There can be zero or more attributes in every element; each one has the the form: attribute_name =‘ attribute_value ’ - There is no space between the name and the “=‘” - Attribute values must be surrounded by “ or ‘ characters Multiple attributes are separated by white space (one or more spaces or tabs). closing tag attribute attribute valuedata open tag element name

16. 16 XML – D ATA AND C OMMENTS … Xml data is any information between an opening and closing tag Xml data must not contain the ‘ ’ characters Comments: closing tag attribute attribute valuedata open tag element name

17. 17 XML – N ESTING & H IERARCHY Xml tags can be nested in a tree hierarchy Xml documents can have only one root tag Between an opening and closing tag you can insert: 1. Data 2. More Elements 3. A combination of data and elements Some Text More

18. 18 X ML – S TORAGE Storage is done just like an n-ary tree (DOM) Some Text More Node Type: Element_Node Name: Element Value: Root Node Type: Element_Node Name: Element Value: tag1 Node Type: Text_Node Name: Text Value: More Node Type: Element_Node Name: Element Value: tag2 Node Type: Text_Node Name: Text Value: Some Text

19. 19 L ECTURE O VERVIEW Internet Concepts Web data formats HTML, XML, DTDs Introduction to three-tier architectures The presentation layer HTML forms; HTTP Get and POST, URL encoding; Javascript; Stylesheets. XSLT The middle tier CGI, application servers, Servlets, JavaServerPages, passing arguments, maintaining state (cookies)

20. 20 DTD – D OCUMENT T YPE D EFINITION A DTD is a schema for Xml data Xml protocols and languages can be standardized with DTD files A DTD says what elements and attributes are required or optional Defines the formal structure of the language

21. 21 DTD – A N E XAMPLE --------------------------------------------------------------------------------

22. 22 DTD - !ELEMENT !ELEMENT declares an element name, and what children elements it should have Content types: Other elements #PCDATA (parsed character data) EMPTY (no content) ANY (no checking inside this structure) A regular expression NameChildren

23. 23 DTD - !ATTLIST <!ATTLIST Orange location CDATA #REQUIRED color ‘orange’> !ATTLIST defines a list of attributes for an element Attributes can be of different types, can be required or not required, and they can have default values. ElementAttributeTypeFlag

24. 24 DTD – W ELL -F ORMED AND V ALID -------------------------------------------------------------------------------- Well-Formed and Valid Not Well-Formed Well-Formed but Invalid Home

25. 25 XML AND DTD S More and more standardized DTDs will be developed MathML Chemical Markup Language Allows light-weight exchange of data with the same semantics Sophisticated query languages for XML are available: Xquery XPath

26. 26 L ECTURE O VERVIEW Internet Concepts Web data formats HTML, XML, DTDs Introduction to three-tier architectures The presentation layer HTML forms; HTTP Get and POST, URL encoding; Javascript; Stylesheets. XSLT The middle tier CGI, application servers, Servlets, JavaServerPages, passing arguments, maintaining state (cookies)

27. 27 C OMPONENTS OF D ATA -I NTENSIVE S YSTEMS Three separate types of functionality: Data management Application logic Presentation The system architecture determines whether these three components reside on a single system (“tier) or are distributed across several tiers

28. 28 S INGLE -T IER A RCHITECTURES All functionality combined into a single tier, usually on a mainframe User access through dumb terminals Advantages: Easy maintenance and administration Disadvantages: Today, users expect graphical user interfaces. Centralized computation of all of them is too much for a central system

29. 29 C LIENT -S ERVER A RCHITECTURES Work division: Thin client Client implements only the graphical user interface Server implements business logic and data management Work division: Thick client Client implements both the graphical user interface and the business logic Server implements data management

30. 30 C LIENT -S ERVER A RCHITECTURES (C ONTD.) Disadvantages of thick clients No central place to update the business logic Security issues: Server needs to trust clients Access control and authentication needs to be managed at the server Clients need to leave server database in consistent state One possibility: Encapsulate all database access into stored procedures Does not scale to more than several 100s of clients Large data transfer between server and client More than one server creates a problem: x clients, y servers: x*y connections

31. 31 T HE T HREE -T IER A RCHITECTURE Presentation tier Middle tier Data management tier

32. 32 T HE T HREE L AYERS Presentation tier Primary interface to the user Needs to adapt to different display devices (PC, PDA, cell phone, voice access?) Middle tier Implements business logic (implements complex actions, maintains state between different steps of a workflow) Accesses different data management systems Data management tier One or more standard database management systems

33. 33 E XAMPLE 1: A IRLINE RESERVATIONS Build a system for making airline reservations What is done in the different tiers? Database System Airline info, available seats, customer info, etc. Application Server Logic to make reservations, cancel reservations, add new airlines, etc. Client Program Log in different users, display forms and human- readable output

34. 34 E XAMPLE 2: C OURSE E NROLLMENT Build a system using which students can enroll in courses Database System Student info, course info, instructor info, course availability, pre-requisites, etc. Application Server Logic to add a course, drop a course, create a new course, etc. Client Program Log in different users (students, staff, faculty), display forms and human-readable output

35. 35 T ECHNOLOGIES Database System (DB2) Application Server (Tomcat, Apache) Client Program (Web Browser) HTML Javascript XSLT JSP Servlets Cookies CGI XML Stored Procedures SQL

36. 36 A DVANTAGES OF THE T HREE -T IER A RCHITECTURE Heterogeneous systems Tiers can be independently maintained, modified, and replaced Thin clients Only presentation layer at clients (web browsers) Integrated data access Several database systems can be handled transparently at the middle tier Central management of connections Scalability Replication at middle tier permits scalability of business logic Software development Code for business logic is centralized Interaction between tiers through well-defined APIs: Can reuse standard components at each tier

37. 37 A PPLICATION S ERVER : P ROCESS S TRUCTURE Process Structure Web BrowserWeb Server Application Server C++ Application JavaBeans DBMS 1 DBMS 2 Pool of Servlets HTTP JDBC ODBC

38. 38 M AINTAINING S TATE HTTP is stateless. Advantages Easy to use: don’t need anything Great for static-information applications Requires no extra memory space Disadvantages No record of previous requests means No shopping baskets No user logins No custom or dynamic content Security is more difficult to implement

39. 39 A PPLICATION S TATE Server-side state Information is stored in a database, or in the application layer’s local memory Client-side state Information is stored on the client’s computer in the form of a cookie Hidden state Information is hidden within dynamically created web pages

40. 40 S ERVER -S IDE S TATE Many types of Server side state: 1. Store information in a database Data will be safe in the database BUT: requires a database access to query or update the information 2. Use application layer’s local memory Can map the user’s IP address to some state BUT: this information is volatile and takes up lots of server main memory

41. 41 S ERVER -S IDE S TATE Should use Server-side state maintenance for information that needs to persist Old customer orders “Click trails” of a user’s movement through a site Permanent choices a user makes

42. 42 C LIENT - SIDE S TATE : C OOKIES Storing text on the client which will be passed to the application with every HTTP request. Can be disabled by the client. Are wrongfully perceived as "dangerous", and therefore will scare away potential site visitors if asked to enable cookies 1 Are a collection of (Name, Value) pairs 1 http://www.webdevelopersjournal.com/columns/stateful.html

43. 43 C LIENT S TATE : C OOKIES Advantages Easy to use in Java Servlets / JSP Provide a simple way to persist non-essential data on the client even when the browser has closed Disadvantages Limit of 4 kilobytes of information Users can (and often will) disable them Should use cookies to store interactive state The current user’s login information The current shopping basket Any non-permanent choices the user has made

44. 44 H IDDEN S TATE Often users will disable cookies You can “hide” data in two places: Hidden fields within a form Using the path information Requires no “storage” of information because the state information is passed inside of each web page

45. 45 H IDDEN S TATE : H IDDEN F IELDS Declare hidden fields within a form: Users will not see this information (unless they view the HTML source) If used prolifically, it’s a killer for performance since EVERY page must be contained within a form.

46. 46 H IDDEN S TATE : P ATH I NFORMATION Path information is stored in the URL request: http://server.com/index.htm?user=jeffd Can separate ‘fields’ with an & character: index.htm?user=jeffd&preference=pepsi There are mechanisms to parse this field in Java, ASP, ASP.NET, PHP

47. 47 M ULTIPLE STATE METHODS Typically all methods of state maintenance are used: User logs in and this information is stored in a cookie User issues a query which is stored in the path information User places an item in a shopping basket cookie User purchases items and credit-card information is stored/retrieved from a database User leaves a click-stream which is kept in a log on the web server (which can later be analyzed)

48. 48 ASP.NET Slides based off:

49. 49 B ACKGROUND - W EB A RCHITECTURE Web Server PC/Mac/Unix/... + Browser Client Server Request: http://www.digimon.com/default.asp Response: …. Network HTTP, TCP/IP

50. 50 ASP.NET O VERVIEW ASP.NET provides services to allow the creation, deployment, and execution of Web Applications and Web Services Like ASP, ASP.NET is a server-side technology Web Applications are built using Web Forms Web Forms are designed to make web-based applications as easy as building Visual Basic applications Web Form = Visual Drag and Drop tools

51. 51 ASP.NET O VERVIEW Simple: less code, easier to create and maintain Multiple, compiled languages Fast Scalable Manageable Customizable and extensible Secure Tool support (Visual Studio.NET)

52. 52 Common Language Specification Common Language Runtime VBC++C# ASP.NET: Web Services and Web Forms JScript… Windows Forms Base Classes ADO.NET: Data and XML Visual Studio.NET ASP.NET O VERVIEW A RCHITECTURE

53. 53 P ROGRAMMING M ODEL Button List Text Browser ASP.NET Button code... List code... Text code... Event handlers Your ASPX Web InterfaceYour C# Code

54. 54 P ROGRAMMING M ODEL A postback occurs when a page generates an HTML form whose values are posted back to the same page A common technique for handling form data In ASP and other server-side technologies the state of the page is lost upon postback... Unless you explicitly write code to maintain state This is tedious, bulky and error-prone

55. 55 P ROGRAMMING M ODEL By default, ASP.NET maintains the state of all server-side controls during a postback Must use method="post“ (in the HTML Form, method=“get”) Server-side control objects are automatically populated during postback No state stored on server Works with all browsers

56. 56 P ROGRAMMING M ODEL Multiple sources of controls Built-in (~ 50 built in!) 3 rd party User-defined Controls range in complexity and power: button, text, drop down, calendar, data grid, ad rotator, validation Can be populated via data binding

57. 57 P ROGRAMMING M ODEL Two styles of creating ASP.NET pages Controls and code in.aspx file Controls in.aspx file, code in code-behind page Supported in Visual Studio.NET Code-behind pages allow you to separate the user interface design from the code Allows programmers and designers to work independently <%@ Codebehind=“WebForm1.cs” Inherits=WebApplication1.WebForm1” %>

58. 58 P ROGRAMMING M ODEL Just edit the code and hit the page ASP.NET will automatically compile the code into an assembly Compiled code is cached in the CLR Subsequent page hits use compiled assembly If the text of the page changes then the code is recompiled Works just like ASP: edit, save and run

59. 59 P ROGRAMMING M ODEL

60. 60 P ROGRAMMING B ASICS The most basic page is just static text Any HTML page can be renamed.aspx Pages may contain: Directives: Server controls: Code blocks: … Data bind expressions: Server side comments:

61. 61 P ROGRAMMING B ASICS Code can respond to page events e.g. Page_Load, Page_Unload Code can respond to control events Button1_Click Textbox1_Changed

62. 62 Example: